1. Field of the Invention
The present invention relates to a medical instrument provided with an insertion body to be inserted into the interior of an object to be examined.
2. Description of the Related Art
As a method of calculating a shape of an insertion portion of an endoscope or the like to be inserted into the interior of an examinee, one using a magnetic field sensor as described in Japanese Patent Application Laid-Open Publication No. 2000-79088 is known. The method using a magnetic field sensor detects a magnetic field from a magnetic field generation coil disposed outside the body of the examinee using a plurality of magnetic field detection coils arranged in an insertion portion and thereby calculates relative positions of the respective magnetic field detection coil with respect to the magnetic field generation coil. Since the positions of the plurality of magnetic field detection coils, that is, the position of the insertion portion, are calculated with reference to the position of the magnetic field generation coil, even if the examinee changes his/her posture or the insertion portion moves, the shape of the insertion portion displayed on a display screen is relatively stable. However, the method using a magnetic field sensor requires the magnetic field generation coil to be installed outside the body of the examinee, which results in an increase in the scale of the system.
By contrast, Japanese Patent Application Laid-Open Publication No. 6-261858 and Japanese Patent Application Laid-Open Publication No. 2007-130151 disclose a method of calculating a shape of an insertion portion by placing a distortion sensor in an insertion portion. Furthermore, Japanese Patent Application Laid-Open Publication No. 2003-515104 and Japanese Patent Application Laid-Open Publication No. 2004-251779 disclose a method of calculating a shape of an insertion portion by detecting distortion of an insertion portion using an optical fiber Bragg grating (Fiber Bragg Grating: hereinafter referred to as “FBG”) sensor.
The method of calculating a shape of an insertion portion based on distortion of the insertion portion does not require a magnetic field generation coil or the like to be installed outside the body of the examinee, and can thereby reduce the size of the system.